Critic's Note: The short version of this movie's plot synopsis is, it's a home-invasion thriller. But it contains a significant twist at about the half-hour mark, and cannot be discussed in any detail without acknowledging said twist. You've been warned.

When last we saw Levi Miller, he was the boy who promised he would never grow up. Now, just two years later, he insists he's grown up already.

Sure, he may only be 12, but, he insists, he's mature for his age. He can pretty much be left home alone already. Check it out, he can even drink alcohol. That, and various other affirmations of manhood touted by boys who have a crush on the babysitter. Perhaps more importantly - again, this is according to Luke (Miller) - he's not just a burgeoning adult, but a really nice guy. Not like those other jerks Ashley (Olivia DeJonge), 17, has been going out with lately. He knows how to treat a woman with kindness and respect. You deserve better.

Surely, Luke believes, this will get through to Ashley. That she'll overlook the five-year age difference and get over the fact that she's been babysitting him since long before his voice dropped, and she'll see him for the knight in shining armor he truly is.

Or, if that doesn't work, plan B: knock her out, tie her up, molest her, and terrorize her for the rest of the night. That'll show her what she's missing.

And so our erstwhile Peter Pan has revealed himself to be not just an entitled, rejected Nice Guy (years ahead of schedule) but a full-blown psychopath to boot. The regular allusions to Home Alone - and all the violence therein - aren't merely for fun. Luke's holiday imprisonment of his beloved Ashley is merely the centerpiece of a much more elaborate set of diabolical plans and contingencies.

Give him credit for this much - there aren't many 12-year-old boys capable of manufacturing this kind of terror and bloodshed. Especially on such a tight schedule. (I mean, Mom and Dad are only supposed to be gone for a few hours. He's supposed to take out all his entitled sexual jealousy and clean up the mess in that window of time? Ambitious, to say the least.) Say what you will about the sadism of Kevin McCallister - who seems to be a sort of role model of Luke's - but at least he was merely reacting to a clear and present danger.

Better Watch Out's nimble shift from a childish realm - in which we're supposed to smile and cringe and feel empathetic embarrassment at this upstart kid's clumsy, out-of-his-league flirting - into more perverse territory reflects the imprecise proximity between prankery and cruelty, between jokes and actions, between fantasies and realities. And how one can easily be mistaken for - and even turn into - the other. We've already begun to suspect Luke is acting a bit too entitled (although, in a 12-year-old sort of way, we think) when ominous noises outside the house, and then inside the house, begin to cast a perilous shadow over what was supposed to be an ordinary evening of babysitting. (Order a pizza, watch a movie, go to bed by 11, the usual.)

And when the supposed intruder turns out to be none other than Luke's best friend and fellow 12-year-old Garrett (The Visit's Ed Oxenbould), Luke comes out looking even worse. But, Olivia can only assume, harmless. Maybe she'll send him to his room. Just a prank - elaborate, yes, but harmless. She's as unimpressed by the effort as she is annoyed at the mischievous lengths the two boys went to just to scare her.

But once the film has reached that point, it wastes no time cutting right to the chase. Once the staged break-in has been exposed, the other ruse vanishes as well: Instead of giving Olivia the chance to call his parents and report him for his naughty behavior, he casually - alarmingly casually - pistol-whips her on the stairwell, knocking her out cold. When she comes to, she's tied to a chair in the kitchen and Luke's precocious persona has suddenly been replaced with something much more menacing.

That moment is a terrific shock pulled off by director Chris Peckover and his co-writer Zack Kahn, and proves they're not content to simply toy with the sexual dynamics - the faux-chivalry, the rescue fantasies, the perception of The Babysitter as a prize for the boy finally coming of age - but are willing to overturn them completely. They want to go big, and painting this kid as merely a brat who reflects male entitlement is far from enough. They take the character to its extreme logical conclusion.

But Peckover's filmmaking doesn't measure up to his bold satirical ambitions. The script keeps pushing things further and further - extending the limits of Luke's malevolence, introducing more characters who find themselves at the kid's mercy, narrowing the margin for error - yet he can't seem to keep up. His visual playbook is thin, and his staging isn't much better. A movie that wants to be twisted and nasty comes across as a milquetoast home-invasion thriller. Peckover never develops an aesthetic to match his ideas.

Which means, as enjoyable as it is in concept and in the quality of its performances, it unavoidably underwhelms, a strong idea with very little execution. For Luke, girls are as abstract a fantasy as the manliness to which he aspires, and the cohabitation of those two - common cinematic fantasies about heroes and rescues, grand romantic gestures and the spoils of the conquering savior - is fertile ground for a perverse lampooning of his (and the audience's) expectations. Better Watch Out is not quite that, but it's somewhere on the right track.